A Temporary Class Drug Notice was put on K2, making it illegal to import, manufacture, sell or supply K2, which contained banned substance EAM-2201.

Some Invercargill stores are still selling K2 after Auckland-based distributor Lightyears Ahead told them the product had a new formula, which it says does not contain EAM-2201.

The "new" K2 packaging is almost identical to the banned product, with no listed ingredients.

A ministry spokesperson said the murkiness surrounding the issue was the reason a permanent psychoactive substances regime would be introduced during the middle of next year.

The onus would be on manufacturers to prove the safety of their products before they were sold.

Although a new K2 was now available, anyone selling it risked possible prosecution because no-one actually knew what was in it, he said.

The ministry considered retailers selling something potentially harmful, with little or no product information was irresponsible, he said.

Retailers needed to weigh the veracity of what they were being told by distributors against the penalties they were exposing themselves to, he said.

Although the ministry, police and health boards monitored reports of harm from unregulated substances, any enforcement action was undertaken by police, he said.

Senior Sergeant Maggie Windle, of Invercargill, said police would work closely with the ministry in relation to the sale of herbal highs to reduce the extremely negative impact they had on the community.

Invercargill area tactical response manager Inspector Olaf Jensen said police were working with Public Health South to enforce the ban on the banned formula and were still dealing with incidents involving the consumption of it.

"It's a concern that we still attend a number of incidents where people are under the influence of K2, displaying psychotic behaviour," he said.

He said manufactures had found a way around the ban by altering the ingredients of K2.

"Police do not have any planned control purchase operations but it wouldn't stop us doing one tomorrow if information came through that sellers were not complying with the legislation," he said.

Public Health South team leader Anne McSoriley said police could investigate and undertake testing of any products suspected of including banned substances.